In a conventional mobile communication system, in an uplink from a mobile station UE to a radio base station Node B, a radio network controller RNC is configured to determine a transmission rate of a dedicated channel in consideration of radio resources of the radio base station Node B, an interference volume in an uplink, a transmission power of the mobile station UE, a transmission processing performance of the mobile station UE, a transmission rate required for an upper application, and the like, and to notify the determined transmission rate of the dedicated channel by a message in a layer-3 (Radio Resource Control Layer) to both of the mobile station UE and the radio base station Node B.
Here, the radio network controller RNC is provided at an upper level of the radio base station Node B, and is an apparatus configured to control the radio base station Node B and the mobile station UE.
In general, data communications often cause burst traffic compared with voice communications or TV communications. Therefore, it is preferable that the transmission rate of a channel used for the data communications is changed fast.
However, as shown in FIG. 11, the radio network controller RNC integrally controls a plurality of radio base stations Node B in general. Therefore, in the conventional mobile communication system, there has been a problem that it is difficult to perform fast control for changing the transmission rate of channel (for example, per approximately 1 through 100 ms), due to processing load, processing delay, or the like.
In addition, in the conventional mobile communication system, there has also been a problem that costs for implementing an apparatus and for operating a network are substantially increased even if the fast control for changing of the transmission rate of the channel can be performed.
Therefore, in the conventional mobile communication system, control for changing the transmission rate of the channel is generally performed on the order from a few hundred ma to a few seconds.
Accordingly, in the conventional mobile communication system, when burst data transmission is performed as shown in FIG. 12(a), the data are transmitted by accepting low-speed, high-delay, and low-transmission efficiency as shown in FIG. 12(b), or, as shown in FIG. 12(c), by reserving radio resources for high-speed communications to accept that radio bandwidth resources in an unoccupied state and hardware resources in the radio base station Node B are wasted.
It should be noted that both of the above-described radio bandwidth resources and hardware resources are applied to the vertical radio resources in FIG. 12.
Therefore, the 3rd Generation Partnership Project (3GPP) and the 3rd Generation Partnership Project 2 (3GPP2), which are international standardization organizations of the third generation mobile communication system, have discussed a method for controlling radio resources at high speed in a layer 1 and a media access control (MAC) sub-layer (a layer-2) between the radio base station Node B and the mobile station UE, so as to utilize the radio resources effectively. Such discussions or discussed functions will be hereinafter referred to as “Enhanced Uplink (EUL)”.
In the EUL, a channel for transmitting a transmission power ratio between an Enhanced Dedicated Physical Data Channel (E-DPDCH) and a Dedicated Physical Control Channel (DPCCH) from a radio base station to each mobile station (i.e., an absolute rate control channel (E-AGCH: EDCH-Absolute Grant Channel)) is defined. (e.g., refer to non-patent document 1)
In addition to the above-described transmission power ratio, the a signal process flag is attached to the E-AGCH. The signal process flag distinguishes between methods in which the E-AGCH is applicable by each HARQ (Hybrid Automatic Repeat Request) processes respectively, and methods in which the E-AGCH is applicable for all of the HARQ processes. (e.g., refer to non-patent document 2)
In this regard, on the E-AGCH, the radio base station masks 16-bit CRC sequence by the identifier of the destination mobile station (E-RNTI: Enhanced-Radio Network Temporary Indicator) and attaches the masking result to information bits (transmission data). Then, the destination mobile station (mobile station identified by the E-RNTI) performs a CRC error detection processing by performing an FEC decoding against the E-AGCH and unmasking the extracted CRC sequence by own E-RNTI. Thus, the destination mobile station enables to detect the status that the signals transmitted to the own station are received correctly.
However, since an impact on the downlink caused by transmitting the E-AGCH is large, there has been a problem that the radio base station cannot transmit transmission data larger than limited number of bits (data size).
Accordingly, it is recommended that the transmission data (information bits) to be mapped to the E-AGCH is limited as 9 to 10 bits at most, thereby the transmission power ratio is reduced. (refer to non-patent document 3)
However, in addition to the above-described transmission power ratio and the signal process flag, a priority level, for example, should be mapped to the E-AGCH as the transmission data. Therefore, there has been a problem that, since the priority level generally has a value between 8 and 16, when the transmission data of 3 to 4 bits are mapped to the E-AGCH, the number of bits of the E-AGCH increases, thereby a required transmission power increases.
(Non-patent Document 1) 3GPP TSG-RAN TS25.211 v6.4.0
(Non-patent Document 2) 3GPP TSG-RAN TS25.309 v0.2.0
(Non-patent Document 3) 3GPP R1-050219